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Fuels and Oils Glossary

The terminology associated with fuels and oils can often be complex and difficult to navigate, making it hard to know which product or service is right for you. Our experts have developed a comprehensive glossary explaining the most frequently used terms, enabling you to make well-informed decisions for your home or business.

If you need further assistance, our technical team are always here to help. Call 0330 123 1144 to get your questions answered by our fuel experts.

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AdBlue

AdBlue is a diesel-exhaust fluid that reduces NOx emissions from diesel-powered engines. It’s filled into a designated tank in the vehicle and is added to the diesel shortly after combustion. AdBlue falls under ISO 22241 specifications and as a trademarked name, all AdBlue suppliers must be VDA-licensed. VDA (Verband der Automobilindustrie) are a German association that ensures AdBlue meets strict industry standards and quality requirements.

AdBlue is also known as AUS 32 or diesel exhaust fluid (DEF).

Additive

A chemical compound added to a fuel to enhance its performance or storage stability. Includes anti-waxing agents, corrosion inhibitors, and detergents.

Alkanes

Saturated hydrocarbons found in crude oil. They form the basis for fuels like petrol and diesel and differ in carbon chain length, affecting their boiling points.

Alternative fuel

Any non-traditional fuel used instead of fossil fuels, e.g. HVO, biodiesel, LNG, CNG.

Anti-wax fuel additive

Many fuels crystalise in cold temperatures which leads to performance issues as a result of waxing. Anti-wax fuel additives improve cold-weather performance and handling properties, resulting in greater fuel efficiency and reduced maintenance costs. It co-crystalises with the fuel to change the shape and size of the crystals formed for improved flow.

Aromatic content

The level of aromatic hydrocarbons in a fuel, affecting combustion quality and emissions.

Aviation fuel

Specialised fuel used to power aircraft. Includes Jet A1 and Avgas (aviation gasoline).

Biodiesel

Biodiesel is also referred to as FAME diesel because it is made from 100% FAME. Derived through the transesterification of vegetable oils and animal fats, FAME biodiesel is a first-generation biofuel that provides environmental benefits over conventional fossil fuels.

Biodiesel comes in a range of forms which includes:

• B7 diesel – A blend of 7% biodiesel with 93% fossil diesel. This is also referred to as ‘road diesel’ and is the fuel that you will find at UK forecourts.
• B100 – 100% FAME biodiesel content
• B20 – A diesel blend containing 20% biodiesel that’s commonly used by businesses looking to reduce diesel emissions without switching to B100

Biofuel

A biofuel is a category of fuels derived from renewable energy sources such water, plants, algae or animal waste. Many fuels fall under the biofuel category such as biodiesel and HVO fuel.

Boiler fuel

A fuel used to generate heat in commercial or industrial boilers, commonly red diesel or kerosene.

British Standard (BS) 2869

BS 2869 is a specification outlined by the British Standards Institution and is the standard set for fuel oils in agricultural, domestic and boilers. BS 2869 has 4 different grades that are optimised towards specific applications.

• Class A2 – Maximum sulphur content of 10ppm (parts per million) for off-road vehicles and equipment
• Class C1 – The standard for premium heating oils for off-grid homes
• Class C2 – The most common class of domestic heating oils for off-grid homes
• Class D – Maximum sulphur content of 1000ppm for heating or static generators

British Standards Institution (BSI)

BSI is the national standards body for the UK. It’s a non-profit organisation that outlines industry standards for a range of products and services.

Bunker fuels

Bunker fuels vary in name and are each suited to different applications. Here’s a list of bunker fuels and their abbreviations:

• MGO – Marine Gas Oil
• MDO – Marine Diesel Oil
• IFO – Intermediate Fuel Oil
• MFO – Marine Fuel Oil
• HFO – Heavy Fuel Oil

Carbon intensity

The amount of CO₂ emitted per unit of energy or fuel used. Lower values indicate cleaner fuels.

Carbon offset fuels

With carbon offset fuels there is no change to the fuel you receive, instead, for a little extra we’ll purchase independently verified carbon credits on your behalf that support carbon-reducing projects across the globe.

Carbon reporting

The process of measuring and disclosing carbon emissions is often broken into Scope 1, 2, and 3 emissions.

Cetane number

The cetane number of a fuel reflects its ignition quality. A fuel with a higher cetane number means that the fuel ignites faster, leading to more efficient combustion and improving engine operation.

Class A2 gas oil

Class A2 gas oil has a maximum sulphur content of 10ppm and is therefore also referred to as ultra-low sulphur gas oil (ULSGO). It falls under BS 2869 specifications and was a common grade of gas oil in the UK, however in recent years there has been a large shift towards EN 590 gas oil which has almost made Class A2 gas oil obsolete.

Class D gas oil

Class D gas oil is a 1000 ppm (parts per million) sulphur content gas oil that meets Grade D BS 2869 specifications. Due to its high sulphur content, it’s predominantly used for heat generation and power generation in older static engines.

Cold filter plugging point (CFPP)

CFPP refers to the lowest temperature at which a fuel can flow through a fuel system without affecting performance. When a fuel reaches it’s CFPP it will start to crystalise and wax which affects it’s ability to pass through fuel systems at maximum performance.

Compressed natural gas (CNG)

A fuel made by compressing natural gas. Used as an alternative to petrol and diesel.

Contaminants

Unwanted substances such as water, microbes, debris or particulates that reduce fuel quality or damage equipment. Our experts have compiled a complete fuel contamination guide if you’d like to learn more.

Crude oil

Unrefined petroleum is extracted from the Earth. It contains a mixture of hydrocarbons and other compounds and is refined through fractional distillation.

Crude oil fractional distillation

Crude oil fractional distillation is a refining process that separates crude oil into components based on boiling points. It is the process used to produce fuels like petrol, diesel, kerosene, and bitumen.

Density

A fuel’s density refers to the mass of fuel contained within a specific volume. Fuels with a higher density are generally more efficient because they carry more energy which also leads to greater fuel efficiency.

Diesel (white diesel/DERV)

Diesel is the most commonly used fuel in automotive, industrial and heating applications. White diesel comes under EN 590 specifications – the European standard for road and off-road vehicles. Due to the wide use and easy access of EN 590 diesel, many industrial fuel systems are also built for EN 590 fuels.

Alternate names for diesel:

• DERV – Which stands for diesel engine road vehicles
• Forecourt diesel – Because this form of diesel is found at UK forecourts
• Fossil diesel – Diesel is made with fossils, which is why it’s sometimes called fossil diesel
• Petrodiesel – As it’s the diesel found at UK petrol stations
• Road diesel – As this diesel is commonly used in road vehicles
• Standard diesel – Due to the fact that this is the most common grade of diesel
• Ultra-Low Sulphur Diesel (ULSD) – Diesel is made with low sulphur content

Diesel bug

A microbial contamination issue caused by bacteria, fungi or yeast at the water-fuel interface in storage tanks. Leads to filter blockages and equipment damage. Our fuel contamination guide can help you understand diesel bug further and help you to prevent it from affecting your fuel systems.

Diesel grades

• Summer grade – Optimised for summer use with a higher viscosity
• Winter grade – Has a lower viscosity than summer grade diesel, meaning it flows easily during cold temperatures and has a lower CFPP

Diesel Secure (anti-theft dye)

Diesel Secure is a dye that’s added to non-rebated fuels to deter thieves and prevent fuel theft by making fuels easy to trace. In April 2022 many businesses lost access to rebated fuels which resulted in them switching to non-rebated fuels that look identical to fuel by regular fuel users. This led to an increase in fuel theft which has increased demand for anti-theft markers.

Drop-in fuel

A fuel that can be used in existing engines or infrastructure without the need for modifications or upgrades.

Emissions

Gases released into the atmosphere by vehicles or machinery typically include methane, CO₂, NOx, SOx, and particulate matter.

Energy density

The amount of energy stored in a given volume of fuel. This is important to check the efficiency of a fuel.

EN (European Standards)

EN refers to European Standards (derived from German translation ‘European Norm’). These standards outline the necessary framework across the European Union. The UK and many other nations also work to European standards as this helps standardise manufacturing processes.

EN 15940

The European standard that specifies the requirements of paraffinic diesels. Fuels that come under EN 15940 include HVO and GTL and are environmentally cleaner alternatives to EN 590 fuels.

EN 14214

The European standard that outlines requirements and test methods for FAME biodiesel and uCOMe biodiesel.

EN 590

EN 590 is a standard outlined by the European Union describing the physical and chemical properties all automotive diesel fuel must meet to be sold in the European Union and other European countries.

EN 590 diesel

EN 590 diesel is also known as road diesel and is the most common diesel supplied in the UK to businesses and forecourts. This is the form of diesel that you will find at petrol stations when filling up a diesel car but this is also used by businesses in vehicle fleets and to fuel diesel-powered industrial equipment.

EN 590 gas oil

EN 590 gas oil is the most common gas oil supplied in the UK and is a marked version of EN 590 diesel. Both fuels have the same properties, the only difference between the two is that EN 590 gas oil is a rebated fuel that is dyed red so that it can be clearly identified. EN 590 gas oil and EN 590 red diesel are terms used interchangeably.

Engine oils

Also referred to as motor oil, engine oil is a lubricant designed to reduce heat, friction and wear of the moving parts within an engine. There are many different types of engine oil for varying applications and temperatures.

EURO 6

A European standard for vehicle emissions. It limits the amount of nitrogen oxides (NOx), hydrocarbons, carbon monoxide (CO), and particulate matter that a vehicle can produce.

FAME

FAME stands for fatty acid methyl esters and they’re esters derived from vegetable oils reacting with methanol. FAME content is often blended with diesel to reduce emissions (all forecourt diesel contains 7% FAME). Some industrial equipment can be fuelled with 100% FAME (also known as biodiesel) however this generally requires fuel system modifications as FAME is known to cause performance issues because FAME attracts moisture which forms sludge over time, particularly in cold temperatures.

Flash point

A flash point is the lowest temperature at which a fuel produces enough flammable vapour to ignite. A low flash point indicates easy ignition but also that the fuel is more hazardous while a high flash point implies a lower fire hazard but more difficult ignition.

Fossil fuels

Fossil fuels are fuels formed from the remains of living organisms and are sourced through drilling and mining. These consist of coal, crude oil and natural gas, which are all used to produce energy and goods.

Fuel additives

Fuel additives are used to improve the performance of your fuel without needing to change the fuel itself. Many people use fuel additives when their fuel is needed for a new application or to extend the life of their equipment.

Fuel duty

A tax levied on fuel. The amount of duty varies as outlined by the government, for instance, red diesel is a rebated fuel while road diesel is subject to the full amount of tax.

Fuel polishing

Fuel polishing is a service that involves restoring contaminated fuel back to pristine condition by circulating it through an advanced filtration system.

Fuel testing

Fuel testing, also referred to as fuel sampling, is the process of taking a small sample of fuel from the top, middle and bottom of your storage tank and testing it for any signs of contamination that may affect performance.

Fuel uplift

A fuel uplift is the process of removing fuel from a tank or fuel system. This service is useful for redundant fuel that is no longer needed or for excess fuel that needs to be transferred to another site.

Gas oil

Gas oil is a common name used to refer to red diesel. It’s a marked fuel that comes in a range of grades and specifications, each tailored to different applications.

Generator fuel

A term used to describe fuel used in generators, such as diesel or HVO fuel. This can also be referred to as backup fuel due to the fact that generators are commonly used for backup power for facilities such as hospitals or data centres.

Green diesel

A name used interchangeably with HVO fuel, a fully renewable alternative to diesel.

Greenhouse gases (GHGs)

Emissions/gases that trap heat in the atmosphere, such as carbon dioxide, methane and nitrous oxide. These gases are the largest contributors to rising global temperatures.

GTL (gas-to-liquid)

GTL is a paraffinic fuel that complies with EN 15940 and is a drop-in alternative to diesel produced from natural gas. It’s a synthetic fuel made through the Fischer-Tropsch process, which converts natural gases into hydrocarbon liquids. GTL helps to reduce net emissions, which is why it’s often used as an alternative to diesel by many businesses.

H2 (hydrogen fuel)

H2 is a clean fuel that produces only water when consumed in a fuel cell. H2 can be produced in a variety of ways, including both through the use of fossil fuels and through renewable energy power.

Heating oil

A collective name for fuels used to heat homes or commercial premises. Kerosene is a form of heating oil used primarily in domestic settings, while diesel or industrial heating oil is often used as commercial heating oil.

Hydraulic oil

Hydraulic oil is a non-compressible fluid used to transfer power and control movement within hydraulic machinery. It’s also known as hydraulic fluid. There are a wide range of hydraulic oils with varying viscosity grades and different classifications, including:

• H and HH – mineral oil-based with no active ingredients
• HL – made with additives to enhance its corrosion protection and improve resistance to ageing
• HLP – made with additional ingredients that reduce wear and increase resistance in areas with mixed friction
• HLPD – stands for High Load, Protection, Detergency and is formulated to protect against wear whilst maintaining cleanliness by removing contaminants
• HM – improves anti-wear in mobile hydraulic systems and provides good resistance to oxidation
• HV and HVLP – hydraulic oils with a high viscosity index for applications where the temperature fluctuates widely

Hydrotreated vegetable oil (HVO fuel)

HVO fuel is a fully renewable and sustainable alternative to diesel that reduces net CO2 emissions by as much as 90%. It’s fully miscible with your existing diesel infrastructure and compatible with all commercially available heating oils. Made from renewable raw materials, HVO gets its name through the hydrotreatment process of vegetable oils, which ensures a consistent product with no esters or contamination. Part of the paraffinic fuel family, HVO adheres to EN 15940 specifications, ASTM D975 and the Fuel Quality Directive 2009/30/EC Annex II. HVO is not to be confused with first-generation biodiesels as it’s FAME-free and an innovative second-generation biofuel.

Alternate names for HVO fuel

• Renewable diesel – as HVO is fully renewable and biodegradable
• HVO100 – when HVO is not blended with any other fuel
• Green diesel – due to the environmentally friendly nature of HVO fuel
• Red HVO – which is rebated HVO (in the same way that red diesel is a rebated form of diesel)

Industrial heating oil (IHO)

Industrial heating oil is a cost-effective alternative to diesel for commercial heating, boiling and drying applications. It’s a rebated fuel which has the same physical properties and calorific value as diesel, meaning you get the same heat output for less money.

Intermittent use

Fuel systems or engines that are not used continuously. These systems require fuel that is more stable and that can be stored for longer durations of time.

ISCC (International Sustainability & Carbon Certification)

The ISCC is a global sustainability certification scheme that covers all renewable feedstocks. It’s among the world’s largest sustainability certification systems.

ISO (International Organisation for Standardisation)

The ISO is an international organisation that brings together experts around the world to find the best way of doing or managing things. They apply their frameworks to a wide range of sectors from banking to pharmaceuticals to transport. Many businesses work to ISO standards as the standards are universally recognised and this helps with clarity and communication, particularly for multinational organisations.

ISO 14064-1

An internationally recognised framework to help organisations and businesses to measure, manage, and report greenhouse gas emissions.

ISO 14068

ISO 14068 is the international framework for carbon neutrality. It provides organisations with guidance to quantify and reduce emissions. It uses a hierarchical approach and which means that businesses must be actively reducing emissions before considering offsetting to achieve the verification.

ISO 22241

ISO 22241 is the international specification that outlines the requirements for the quality, handling and storage of AdBlue.

ISO 8217

ISO 8217 is an international framework that outlines the requirements for fuels in marine engines and boilers.

ISO VG

The ISO VG is an international framework for viscosity grades. It aims to create standardised guidance for viscosity grades for manufacturers of oils and lubricants across the world.

Jet A1 (jet fuel)

Jet A1 is the most commonly used aviation fuel. It is highly refined kerosene with enhanced additives that make it more suitable for aircraft.

Kerosene

Coming under Class C2 BS 2869 specifications, kerosene is commonly used by domestic fuel users to heat off-grid homes. It’s a non-corrosive fuel, which makes it less dangerous than other types of fuel and therefore more suitable for domestic use.

Alternative names for kerosene

• Home heating oil
• Kero
• C2 kero
• 28-second burning oil
• Burning oil
• Fuel oil

Kerosene lubricity additive

Kerosene lubricity additive reduces wear in heating systems and fuel pumps to increase equipment longevity. It may also be added when kerosene is intended to be used in place of diesel for stationery equipment.

Kinematic viscosity

The kinematic viscosity is a fuel’s resistance to flow under the weight of gravity. This is a useful measure to businesses whose fuel systems apply no external forces to the fuel when in use.

Kleenburn kerosene

Kleenburn kerosene, also known as carbon clean kerosene or premium kerosene, is a more environmentally friendly alternative to regular kerosene that reduces emissions whilst improving the reliability, performance and longevity of home heating systems. It meets Class C1 BS 2869 standards and reduces fuel consumption by approximately 10%, saving users on their heating costs.

Liquefied petroleum gas (LPG)

LPG is a colourless and highly flammable gas that can be stored and compressed for later use. It is made up of propane and butane and it’s a key component of natural gas. It is predominantly used for domestic heating and cooking as well as a lighter fuel.

Liquefied natural gas (LNG)

LNG is natural gas that has been cooled to a liquid form and it’s part of the UK energy mix. It’s used for a range of tasks such as heating homes, fueling transport and in manufacturing (both as a fuel and as a raw material).

Lubricant

A lubricant is any oil or grease used to reduce friction and wear between moving parts in machinery, equipment or engines. There is a wide range of lubricants which vary in thickness and flow, giving each lubricant unique properties that make them suitable for different applications. Lubricants can be made from a range of base oils, which you can find below.

• Mineral oil – sourced from natural minerals such as refined crude petroleum
• Synthetic oil – chemically modified compounds with enhanced properties
• Semi-synthetic oil – a blend of both mineral and synthetic oils

Lubricity

Lubricity is a property of an oil which determines the amount of wear and tear that can be prevented. An oil’s lubricity is measured in micrometres (μm), calculated by measuring the wear scar diameter (WSD) against a test ball.

Marine gas oil

Marine gas oil is a low-sulphur bunker fuel used for heat generation and to propel marine vessels.

Microbial contamination

A form of contamination where bacteria, fungi or yeast grows within a fuel tank, often as a result of water mixing with fuel. Microbial contamination can be cleaned and removed to prevent fuel filters clogging and damage to fuel tanks or fuel systems.

Net zero

Net zero is the balance between emitted emissions and removed emissions. It’s a goal for the UK and organisations to reach by reducing, removing or capturing emissions.

Off-road fuel use

Refers to use of rebated fuels off-road within sectors that are permitted to use it.

OFTEC

OFTEC are an organisation that sets out standards across the heating and cooking industries within the UK. They work closely with the government and certification bodies to promote the highest professional and technical standards. They provide guidance to homes and businesses to store and use fuel safely.

Oil tank monitoring

A remote system attached to a fuel tank is used to monitor fuel levels remotely. These monitoring systems submit fuel data to satellites via cellular technology so that the information can be viewed on an online dashboard.

Oxidation stability

Oxidation stability is a fuel’s ability to resist degradation when exposed to oxygen. A fuel with a greater oxygen stability can be stored for longer periods of time, which can make it more suitable for backup generators.

Paraffin

A highly refined and distilled version of kerosene that produces less soot when burned.

Paraffinic diesel

Paraffinic diesels are cleaner diesel alternatives that produce lower emissions whilst operating within existing fuel infrastructure. Paraffinic diesels include HVO and GTL which are known for having near-zero sulphur and aromatic content whilst being fossil-free.

Particulate matter

Particulate matter is everything in the air that is not a gas, including dirt, soot, ash and dust.

PAS 2060

An international standard created by the British Standards Institution (BSI) that outlines guidance for demonstrating carbon neutrality. This framework has now been replaced by ISO 14068 in 2025, a more robust framework for managing and monitoring carbon neutrality.

Petrol

Also known as gasoline or petroleum and is primarily used in spark-ignition engines.

Priority fuel contracts

Often referred to as emergency fuel contracts, a priority fuel contract guarantees your fuel supply within a pre-agreed timeframe in the event of an emergency.

RDCO (Registered Dealer in Controlled Oils)

RDCO is an HMRC-managed scheme that requires all dealers of controlled oils to register and comply with specific obligations. A business must be registered and comply with these obligations to buy or sell rebated fuels such as red diesel or kerosene.

Red diesel (gas oil)

Red diesel is exactly the same fuel as diesel, but it is dyed red to differentiate the fuel for tax purposes. While standard diesel is subject to the full fuel tax rate, red diesel is a rebated fuel that allows eligible users to pay less tax on their fuel.

Alternate names for red diesel

• Gas oil – due to the heating applications that red diesel is generally used in
• Agricultural diesel – as farmers are the largest consumers of red diesel
• Tractor diesel – for the same reason, it’s referred to as agricultural diesel, red diesel is often used in tractors
• Marked diesel – due to the fact that it is dyed red
• Off-road diesel – as it’s not allowed to be used on UK roads
• Rebated diesel – as red diesel benefits from rebated tax benefits

Renewable Fuels Assurance Scheme (RFAS)

The Renewable Fuels Assurance Scheme is an independent initiative managed by Zemo and works alongside the government’s RTFO. The core objective of the scheme is to verify claims by companies supplying renewable fuels.

Renewable Transport Fuel Obligation (RTFO)

The RTFO is a UK government scheme that requires suppliers of transport fuel to meet an annual obligation for the supply of low-carbon fuels.

Scope 1, 2 & 3 emissions

Categories used in carbon reporting:

• Scope 1 – Direct emissions from owned sources (such as fuel consumption or emissions from industrial processes)
• Scope 2 – Indirect emissions from purchased energy (such as electricity or heating)
• Scope 3 – Indirect emissions from supply chain and customer use (such as lifetime emissions of a product)

Selective catalytic reduction (SCR)

A technology used to reduce NOx emissions in diesel exhausts. It involves adding a reduction agent before being processed through a catalytic converter and leaving the exhaust. AdBlue added to diesel is an example of SCR technology.

Sludge

Residue that forms at the bottom of storage tanks due to fuel degradation or microbial activity. Sludge can be formed as a result of contaminants such as water entering your tank or from changes in temperature.

Storage stability

The ability of fuel to resist breakdown during long-term storage. Fuels with FAME content or that are exposed to contaminants typically have lower storage stability, making FAME-free fuels such as HVO more suitable for long-term storage.

Sulphur content

The amount of sulphur present within a fuel. Sulphur content cause air pollutants and can damage engines which is why most UK fuels road fuels are produced with ultra-low sulphur content.

Tank cleaning

The process of cleaning a fuel tank to remove any sludge or debris externally or internally via man-entry.

Tank decommissioning

Tank decommissioning is the process of safely putting a fuel tank out of service. This involves degassing the tank and completely filling it with foam or concrete to prevent it from regassing over time. Tank decommissioning can put the tank out of service both permanently and temporarily via foam filling.

Tank telemetry monitoring system

Tank telemetry monitoring systems are small devices that are installed on your fuel tank, which allow you to remotely monitor your fuel levels online. The telemetry device uploads the fuel data online via cellular technology so that you can view fuel levels remotely, whilst providing valuable insights into your consumption history.

Transesterification

The chemical process of producing biodiesel by combining alcohol with renewable sources such as animal fats, vegetable oils or waste cooking oils.

Viscosity

The viscosity of a fuel or oil describes its flow properties, such as how thick or thin an oil is. An oil with a high viscosity means that it is thicker and therefore flows slowly, while a low viscosity means that the oil is thin and easily flows. Oils with different viscosities can be used for different purposes, for instance, a low viscosity oil may be more suitable in colder temperatures while a high viscosity oil may be suitable for warmer temperatures.

Viscosity index

Viscosity index refers to the change of an oil’s viscosity at different temperatures. A high viscosity index means that the viscosity is more stable across a broader range of temperatures whist a low viscosity index indicates that the viscosity changes quickly as the temperature changes.

Waste oil collection

This service involves uplifting redundant fuels and removing or transferring it from a site. If the fuel is no longer needed and suitable to be put back into use, we may buy your fuel back from you.

Zero-emission vehicle

A vehicle that produces no tailpipe emissions, such as an electric battery-powered vehicle or a hydrogen fuel-powered vehicle.

Hopefully, our glossary of the common terminology used within the fuels and oils sector has helped you to get a better understanding. However, should you have further questions about any of the fuels and oils or lubricants that you or your business requires. Give our fuel experts a call today on 0330 123 1144.